Dangerous CV Drug-Drug Interactions: A 5-question Quiz
Cardiovascular medications are widely-prescribed in the US. Alex Evans, PharmD, MBA, drafted questions on the top 5 dangerous interactions he sees regularly in practice.
Medications for cardiovascular disease dominate the list of most widely-prescribed drugs in the US, and there's no doubt you probably prescribe them nearly every day in your practice. However, lurking behind some of those therapies are dangerous drug interactions. This quiz covers the top 5 interactions I see regularly in my practice as a community pharmacist.
1. What is the maximum dose of simvastatin a patient should be on while also taking amlodipine?
2. Which of the medications above is/are contraindicated with dofetilide (Tikosyn)?
Answer E. All of the above. Hydrochlorothiazide, verapamil, trimethoprim (including in combination products), and ketoconazole can increase dofetilide concentrations. This can lead to an increase in the QTc interval, putting the patient at risk for Torsades de Pointes. Cimetidine, dolutegravir, and prochlorperazine also are contraindicated with dofetilide. After initial dose, dofetilide should be discontinued anytime QT or QTc >500 msec.
3. When a patient on digoxin is started on amiodarone, what is the most appropriate action?
Answer: C. Reduce dose of digoxin by 50%. When starting amiodarone, either reduce the digoxin dose by 50% or discontinued the drug (if warranted). Amiodarone has been shown to more than double digoxin concentrations.
4. Which of the drugs above can interact with lithium? (More than one may apply)
Answer: A, B, and C (ACE inhibitors, ARBs, and thiazide diuretics). ACE inhibitors, ARBs, and thiazide diuretics can all reduce lithium clearance, resulting in increased lithium concentrations.
5. How long should a patient wait after taking sildenafil before taking nitrates?
Anwer: D. 24 hours. Although nitrates are contraindicated when taken with sildenafil, there is some evidence they can be used safely in the same patient if they are separated by at least 24 hours. An American College of Cardiology Expert Consensus provides in-depth guidelines on the use of sildenafil with nitrate products.
Key Points on Sildenafil/Nitrates
• Sildenafil is absolutely contraindicated within 24 hours of any nitrate use and vice-versa.
• Sildenafil should not be prescribed in patients on long-acting nitrates.
• All patients taking nitrates should be counseled on the interaction.
• Sildenafil is frequently obtained from other doctors, friends, through the mail, etc.
Additional Key Points on Sildenafil/Nitratres
• In patients who still have angina after using sildenafil, consider beta-blockers or other non-nitrate alternatives.
• In patients on sildenafil experiencing an acute MI, nitrates should be excluded from the MI treatment regimen.
• Patients with reduced clearance of sildenafil (CrCl <30mL/min, hepatic dysfunction, on CYP3A4 inhibitors) might need an interval longer than 24 hours.
